The viruses that cause ordinary colds are all quite species-specific. Dogs can’t catch human colds (or vice versa), but they do have their own version, called canine infectious tracheobronchitis or kennel cough. The influenza virus is much more adaptable though. Bird, pig, horse, dog and human flu have all been shown to jump the species barrier. And bacterial diseases are even more contagious. Cats and dogs can both catch tuberculosis from humans, for example.